Remove url from a given string in C#

If you are looking for a non RegEx way to do this, here you go. But the method I encoded below assumes that a URL begins with "http://" or "https://", which means it will not work with URL's that begin with something like ftp:// or file://, although the code below can be easily modified to support that. Also, it assumes the URL path continues until it reaches either the end of the string or a white space character (like a space or a tab or a new line). Again, this can easily be modified if your requirements are different.

Also, if the string contains no URL, currently it just returns a blank string. You can modify this easily too!

using System;

public class Program
{
    public static void Main()
    {
        string str = "I saw a cat and a horse on https://www.youtube.com/";

        UrlExtraction extraction = RemoveUrl(str);
        Console.WriteLine("Original Text: " + extraction.OriginalText);
        Console.WriteLine();
        Console.WriteLine("Url: " + extraction.ExtractedUrl);
        Console.WriteLine("Text: " + extraction.TextWithoutUrl);
    }

    private static UrlExtraction RemoveUrl(string str)
    {       
        if (String.IsNullOrWhiteSpace(str))
        {
            return new UrlExtraction("", "", "");
        }

        int startIndex = str.IndexOf("https://", 
                StringComparison.InvariantCultureIgnoreCase);

        if (startIndex == -1)
        {
            startIndex = str.IndexOf("http://", 
                StringComparison.InvariantCultureIgnoreCase);
        }

        if (startIndex == -1)
        {
            return new UrlExtraction(str, "", "");
        }

        int endIndex = startIndex;
        while (endIndex < str.Length && !IsWhiteSpace(str[endIndex])) 
        {           
            endIndex++;
        }

        return new UrlExtraction(str, str.Substring(startIndex, endIndex - startIndex), 
            str.Remove(startIndex, endIndex - startIndex));
    }

    private static bool IsWhiteSpace(char c)
    {
        return 
            c == '\n' || 
            c == '\r' || 
            c == ' ' || 
            c == '\t';
    }

    private class UrlExtraction
    {
        public string ExtractedUrl {get; set;}
        public string TextWithoutUrl {get; set;}
        public string OriginalText {get; set;}

        public UrlExtraction(string originalText, string extractedUrl, 
            string textWithoutUrl)
        {
            OriginalText = originalText;
            ExtractedUrl = extractedUrl;
            TextWithoutUrl = textWithoutUrl;
        }
    }
}

A simplified version of what you're doing. Instead of using SubString or IndexOf, I split the input into a list of strings, and remove the items that contain a URL. I iterate over the list in reverse as removing an item in a forward loop direction will skip an index.

    public static string RemoveUrl(string input)
    {
        List<string> words = input.Split(" ").ToList();
        for (int i = words.Count - 1; i >= 0; i--) 
        {
            if (words[i].StartsWith("https://")) words.RemoveAt(i);
        }
        return string.Join(" ", words);
    }

This methods advantage is avoiding SubString and Replace methods that essentially create new Strings each time they're used. In a loop this excessive string manipulation can put pressure on the Garbage Collector and bloat the Managed Heap. A Split and Join has less performance cost in comparison especially when used in a loop like this with a lot of data.

@Moshi is correct with large amounts of data, so this is more of a Production Code Base example:

public static class Ext
{
    public static LinkedList<T> RemoveAll<T>(this LinkedList<T> list, Predicate<T> match)
    {
        if (list == null)
        {
            throw new ArgumentNullException("list");
        }
        if (match == null)
        {
            throw new ArgumentNullException("match");
        }
        var count = 0;
        var node = list.First;
        while (node != null)
        {
            var next = node.Next;
            if (match(node.Value))
            {
                list.Remove(node);
                count++;
            }
            node = next;
        }
        return list;
    }
}

public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();
        var s= "I saw a https://www.youtube.com/cat and a https://www.youtube.com/horse on https://www.youtube.com/";

        //Uncomment for second run 
        //s= @"I saw a https://www.youtube.com/cat and a https://www.youtube.com/horse on https://www.youtube.com/
        //but it doesnt work
        //what I want to achieve is remove the entire https://www.youtube.com/ and display I saw a cat and a horse on
        //I also want to display a message like the sentence you input doesn't have url if the sentence doesn't have any url.";

        Stopwatch watch = new Stopwatch();

        watch.Start();
        var resultList = RemoveUrl(s);
        watch.Stop(); Debug.WriteLine(watch.Elapsed.ToString());

        watch.Reset(); watch.Start();
        var wordsLL = new LinkedList<string>(s.Split(' '));
        var result = string.Join(' ', wordsLL.RemoveAll(x => x.StartsWith("https://")));
        watch.Stop(); Debug.WriteLine(watch.Elapsed.ToString());
       }
 }

var s one line:
watch.Elapsed = {00:00:00.0116388}
watch.Elapsed = {00:00:00.0134778}

var s multilines:
watch.Elapsed = {00:00:00.0013588}
watch.Elapsed = {00:00:00.0009252}

Better way to use, split and StringBuilder. Code will be look like this. StringBuilder is optimized this kind of situation.

Pseudocode:

    var words = "I saw a cat and a horse on https://www.youtube.com/".Split(" ").ToList();
    var sb = new StringBuilder();
    foreach(var word in words){
        if(!word.StartsWith("https://")) sb.Append(word + " ");
    }
    return sb.ToString();